[DebugInfo] Add num_extra_inhabitants to debug info

An extra inhabitant is a bit pattern that does not represent a valid
value for instances of a given type. The number of extra inhabitants is
the number of those bit configurations.

This is used by Swift to save space when composing types. For example,
because Bool only needs 2 bit patterns to represent all of its values
(true and false), an Optional<Bool> only occupies 1 byte in memory by
using a bit configuration that is unused by Bool. Which bit patterns are
unused are part of the ABI of the language.

Since Swift generics are not monomorphized, by using dynamic libraries
you can have generic types whose size, alignment, etc, are known only
at runtime (which is why this feature is needed).

This patch adds num_extra_inhabitants to LLVM-IR debug info and in DWARF
as an Apple extension.

Author: augusto2112

llvm/include/llvm/BinaryFormat/Dwarf.def

@@ -636,6 +636,7 @@ HANDLE_DW_AT(0x3fed, APPLE_property, 0, APPLE)
 HANDLE_DW_AT(0x3fee, APPLE_objc_direct, 0, APPLE)
 HANDLE_DW_AT(0x3fef, APPLE_sdk, 0, APPLE)
 HANDLE_DW_AT(0x3ff0, APPLE_origin, 0, APPLE)
+HANDLE_DW_AT(0x3ff1, APPLE_num_extra_inhabitants, 0, APPLE)
 
 // Attribute form encodings.
 HANDLE_DW_FORM(0x01, addr, 2, DWARF)

llvm/include/llvm/IR/DIBuilder.h

@@ -225,9 +225,13 @@ namespace llvm {
     /// \param SizeInBits  Size of the type.
     /// \param Encoding    DWARF encoding code, e.g., dwarf::DW_ATE_float.
     /// \param Flags       Optional DWARF attributes, e.g., DW_AT_endianity.
+    /// \param NumExtraInhabitants The number of extra inhabitants of the type.
+    /// An extra inhabitant is a bit pattern that does not represent a valid
+    /// value for instances of a given type.
     DIBasicType *createBasicType(StringRef Name, uint64_t SizeInBits,
                                  unsigned Encoding,
-                                 DINode::DIFlags Flags = DINode::FlagZero);
+                                 DINode::DIFlags Flags = DINode::FlagZero,
+                                 uint32_t NumExtraInhabitants = 0);
 
     /// Create debugging information entry for a string
     /// type.
@@ -484,11 +488,15 @@ namespace llvm {
     /// \param Elements     Struct elements.
     /// \param RunTimeLang  Optional parameter, Objective-C runtime version.
     /// \param UniqueIdentifier A unique identifier for the struct.
+    /// \param NumExtraInhabitants The number of extra inhabitants of the type.
+    /// An extra inhabitant is a bit pattern that does not represent a valid
+    /// value for instances of a given type.
     DICompositeType *createStructType(
         DIScope *Scope, StringRef Name, DIFile *File, unsigned LineNumber,
         uint64_t SizeInBits, uint32_t AlignInBits, DINode::DIFlags Flags,
         DIType *DerivedFrom, DINodeArray Elements, unsigned RunTimeLang = 0,
-        DIType *VTableHolder = nullptr, StringRef UniqueIdentifier = "");
+        DIType *VTableHolder = nullptr, StringRef UniqueIdentifier = "",
+        uint32_t NumExtraInhabitants = 0);
 
     /// Create debugging information entry for an union.
     /// \param Scope        Scope in which this union is defined.

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -712,31 +712,38 @@ class DIType : public DIScope {
   DIFlags Flags;
   uint64_t SizeInBits;
   uint64_t OffsetInBits;
+  uint32_t NumExtraInhabitants;
 
 protected:
   DIType(LLVMContext &C, unsigned ID, StorageType Storage, unsigned Tag,
          unsigned Line, uint64_t SizeInBits, uint32_t AlignInBits,
-         uint64_t OffsetInBits, DIFlags Flags, ArrayRef<Metadata *> Ops)
+         uint64_t OffsetInBits, uint32_t NumExtraInhabitants, DIFlags Flags,
+         ArrayRef<Metadata *> Ops)
       : DIScope(C, ID, Storage, Tag, Ops) {
-    init(Line, SizeInBits, AlignInBits, OffsetInBits, Flags);
+    init(Line, SizeInBits, AlignInBits, OffsetInBits, NumExtraInhabitants,
+         Flags);
   }
   ~DIType() = default;
 
   void init(unsigned Line, uint64_t SizeInBits, uint32_t AlignInBits,
-            uint64_t OffsetInBits, DIFlags Flags) {
+            uint64_t OffsetInBits, uint32_t NumExtraInhabitants,
+            DIFlags Flags) {
     this->Line = Line;
     this->Flags = Flags;
     this->SizeInBits = SizeInBits;
     this->SubclassData32 = AlignInBits;
     this->OffsetInBits = OffsetInBits;
+    this->NumExtraInhabitants = NumExtraInhabitants;
   }
 
   /// Change fields in place.
   void mutate(unsigned Tag, unsigned Line, uint64_t SizeInBits,
-              uint32_t AlignInBits, uint64_t OffsetInBits, DIFlags Flags) {
+              uint32_t AlignInBits, uint64_t OffsetInBits,
+              uint32_t NumExtraInhabitants, DIFlags Flags) {
     assert(isDistinct() && "Only distinct nodes can mutate");
     setTag(Tag);
-    init(Line, SizeInBits, AlignInBits, OffsetInBits, Flags);
+    init(Line, SizeInBits, AlignInBits, OffsetInBits, NumExtraInhabitants,
+         Flags);
   }
 
 public:
@@ -749,6 +756,7 @@ class DIType : public DIScope {
   uint32_t getAlignInBits() const;
   uint32_t getAlignInBytes() const { return getAlignInBits() / CHAR_BIT; }
   uint64_t getOffsetInBits() const { return OffsetInBits; }
+  uint32_t getNumExtraInhabitants() const { return NumExtraInhabitants; }
   DIFlags getFlags() const { return Flags; }
 
   DIScope *getScope() const { return cast_or_null<DIScope>(getRawScope()); }
@@ -820,49 +828,63 @@ class DIBasicType : public DIType {
 
   DIBasicType(LLVMContext &C, StorageType Storage, unsigned Tag,
               uint64_t SizeInBits, uint32_t AlignInBits, unsigned Encoding,
-              DIFlags Flags, ArrayRef<Metadata *> Ops)
+              uint32_t NumExtraInhabitants, DIFlags Flags,
+              ArrayRef<Metadata *> Ops)
       : DIType(C, DIBasicTypeKind, Storage, Tag, 0, SizeInBits, AlignInBits, 0,
-               Flags, Ops),
+               NumExtraInhabitants, Flags, Ops),
         Encoding(Encoding) {}
   ~DIBasicType() = default;
 
   static DIBasicType *getImpl(LLVMContext &Context, unsigned Tag,
                               StringRef Name, uint64_t SizeInBits,
                               uint32_t AlignInBits, unsigned Encoding,
-                              DIFlags Flags, StorageType Storage,
-                              bool ShouldCreate = true) {
+                              uint32_t NumExtraInhabitants, DIFlags Flags,
+                              StorageType Storage, bool ShouldCreate = true) {
     return getImpl(Context, Tag, getCanonicalMDString(Context, Name),
-                   SizeInBits, AlignInBits, Encoding, Flags, Storage,
-                   ShouldCreate);
+                   SizeInBits, AlignInBits, Encoding, NumExtraInhabitants,
+                   Flags, Storage, ShouldCreate);
   }
   static DIBasicType *getImpl(LLVMContext &Context, unsigned Tag,
                               MDString *Name, uint64_t SizeInBits,
                               uint32_t AlignInBits, unsigned Encoding,
-                              DIFlags Flags, StorageType Storage,
-                              bool ShouldCreate = true);
+                              uint32_t NumExtraInhabitants, DIFlags Flags,
+                              StorageType Storage, bool ShouldCreate = true);
 
   TempDIBasicType cloneImpl() const {
     return getTemporary(getContext(), getTag(), getName(), getSizeInBits(),
-                        getAlignInBits(), getEncoding(), getFlags());
+                        getAlignInBits(), getEncoding(),
+                        getNumExtraInhabitants(), getFlags());
   }
 
 public:
   DEFINE_MDNODE_GET(DIBasicType, (unsigned Tag, StringRef Name),
-                    (Tag, Name, 0, 0, 0, FlagZero))
+                    (Tag, Name, 0, 0, 0, 0, FlagZero))
   DEFINE_MDNODE_GET(DIBasicType,
                     (unsigned Tag, StringRef Name, uint64_t SizeInBits),
-                    (Tag, Name, SizeInBits, 0, 0, FlagZero))
+                    (Tag, Name, SizeInBits, 0, 0, 0, FlagZero))
   DEFINE_MDNODE_GET(DIBasicType,
                     (unsigned Tag, MDString *Name, uint64_t SizeInBits),
-                    (Tag, Name, SizeInBits, 0, 0, FlagZero))
+                    (Tag, Name, SizeInBits, 0, 0, 0, FlagZero))
   DEFINE_MDNODE_GET(DIBasicType,
                     (unsigned Tag, StringRef Name, uint64_t SizeInBits,
                      uint32_t AlignInBits, unsigned Encoding, DIFlags Flags),
-                    (Tag, Name, SizeInBits, AlignInBits, Encoding, Flags))
+                    (Tag, Name, SizeInBits, AlignInBits, Encoding, 0, Flags))
   DEFINE_MDNODE_GET(DIBasicType,
                     (unsigned Tag, MDString *Name, uint64_t SizeInBits,
                      uint32_t AlignInBits, unsigned Encoding, DIFlags Flags),
-                    (Tag, Name, SizeInBits, AlignInBits, Encoding, Flags))
+                    (Tag, Name, SizeInBits, AlignInBits, Encoding, 0, Flags))
+  DEFINE_MDNODE_GET(DIBasicType,
+                    (unsigned Tag, StringRef Name, uint64_t SizeInBits,
+                     uint32_t AlignInBits, unsigned Encoding,
+                     uint32_t NumExtraInhabitants, DIFlags Flags),
+                    (Tag, Name, SizeInBits, AlignInBits, Encoding,
+                     NumExtraInhabitants, Flags))
+  DEFINE_MDNODE_GET(DIBasicType,
+                    (unsigned Tag, MDString *Name, uint64_t SizeInBits,
+                     uint32_t AlignInBits, unsigned Encoding,
+                     uint32_t NumExtraInhabitants, DIFlags Flags),
+                    (Tag, Name, SizeInBits, AlignInBits, Encoding,
+                     NumExtraInhabitants, Flags))
 
   TempDIBasicType clone() const { return cloneImpl(); }
 
@@ -890,7 +912,7 @@ class DIStringType : public DIType {
                uint64_t SizeInBits, uint32_t AlignInBits, unsigned Encoding,
                ArrayRef<Metadata *> Ops)
       : DIType(C, DIStringTypeKind, Storage, Tag, 0, SizeInBits, AlignInBits, 0,
-               FlagZero, Ops),
+               0, FlagZero, Ops),
         Encoding(Encoding) {}
   ~DIStringType() = default;
 
@@ -1016,7 +1038,7 @@ class DIDerivedType : public DIType {
                 std::optional<PtrAuthData> PtrAuthData, DIFlags Flags,
                 ArrayRef<Metadata *> Ops)
       : DIType(C, DIDerivedTypeKind, Storage, Tag, Line, SizeInBits,
-               AlignInBits, OffsetInBits, Flags, Ops),
+               AlignInBits, OffsetInBits, 0, Flags, Ops),
         DWARFAddressSpace(DWARFAddressSpace) {
     if (PtrAuthData)
       SubclassData32 = PtrAuthData->RawData;
@@ -1157,39 +1179,43 @@ class DICompositeType : public DIType {
 
   DICompositeType(LLVMContext &C, StorageType Storage, unsigned Tag,
                   unsigned Line, unsigned RuntimeLang, uint64_t SizeInBits,
-                  uint32_t AlignInBits, uint64_t OffsetInBits, DIFlags Flags,
+                  uint32_t AlignInBits, uint64_t OffsetInBits,
+                  uint32_t NumExtraInhabitants, DIFlags Flags,
                   ArrayRef<Metadata *> Ops)
       : DIType(C, DICompositeTypeKind, Storage, Tag, Line, SizeInBits,
-               AlignInBits, OffsetInBits, Flags, Ops),
+               AlignInBits, OffsetInBits, NumExtraInhabitants, Flags, Ops),
         RuntimeLang(RuntimeLang) {}
   ~DICompositeType() = default;
 
   /// Change fields in place.
   void mutate(unsigned Tag, unsigned Line, unsigned RuntimeLang,
               uint64_t SizeInBits, uint32_t AlignInBits, uint64_t OffsetInBits,
-              DIFlags Flags) {
+              uint32_t NumExtraInhabitants, DIFlags Flags) {
     assert(isDistinct() && "Only distinct nodes can mutate");
     assert(getRawIdentifier() && "Only ODR-uniqued nodes should mutate");
     this->RuntimeLang = RuntimeLang;
-    DIType::mutate(Tag, Line, SizeInBits, AlignInBits, OffsetInBits, Flags);
+    DIType::mutate(Tag, Line, SizeInBits, AlignInBits, OffsetInBits,
+                   NumExtraInhabitants, Flags);
   }
 
   static DICompositeType *
   getImpl(LLVMContext &Context, unsigned Tag, StringRef Name, Metadata *File,
           unsigned Line, DIScope *Scope, DIType *BaseType, uint64_t SizeInBits,
-          uint32_t AlignInBits, uint64_t OffsetInBits, DIFlags Flags,
-          DINodeArray Elements, unsigned RuntimeLang, DIType *VTableHolder,
+          uint32_t AlignInBits, uint64_t OffsetInBits,
+          uint32_t NumExtraInhabitants, DIFlags Flags, DINodeArray Elements,
+          unsigned RuntimeLang, DIType *VTableHolder,
           DITemplateParameterArray TemplateParams, StringRef Identifier,
           DIDerivedType *Discriminator, Metadata *DataLocation,
           Metadata *Associated, Metadata *Allocated, Metadata *Rank,
           DINodeArray Annotations, StorageType Storage,
           bool ShouldCreate = true) {
-    return getImpl(
-        Context, Tag, getCanonicalMDString(Context, Name), File, Line, Scope,
-        BaseType, SizeInBits, AlignInBits, OffsetInBits, Flags, Elements.get(),
-        RuntimeLang, VTableHolder, TemplateParams.get(),
-        getCanonicalMDString(Context, Identifier), Discriminator, DataLocation,
-        Associated, Allocated, Rank, Annotations.get(), Storage, ShouldCreate);
+    return getImpl(Context, Tag, getCanonicalMDString(Context, Name), File,
+                   Line, Scope, BaseType, SizeInBits, AlignInBits, OffsetInBits,
+                   Flags, Elements.get(), RuntimeLang, VTableHolder,
+                   TemplateParams.get(),
+                   getCanonicalMDString(Context, Identifier), Discriminator,
+                   DataLocation, Associated, Allocated, Rank, Annotations.get(),
+                   NumExtraInhabitants, Storage, ShouldCreate);
   }
   static DICompositeType *
   getImpl(LLVMContext &Context, unsigned Tag, MDString *Name, Metadata *File,
@@ -1199,7 +1225,8 @@ class DICompositeType : public DIType {
           Metadata *VTableHolder, Metadata *TemplateParams,
           MDString *Identifier, Metadata *Discriminator, Metadata *DataLocation,
           Metadata *Associated, Metadata *Allocated, Metadata *Rank,
-          Metadata *Annotations, StorageType Storage, bool ShouldCreate = true);
+          Metadata *Annotations, uint32_t NumExtraInhabitants,
+          StorageType Storage, bool ShouldCreate = true);
 
   TempDICompositeType cloneImpl() const {
     return getTemporary(
@@ -1208,7 +1235,7 @@ class DICompositeType : public DIType {
         getFlags(), getElements(), getRuntimeLang(), getVTableHolder(),
         getTemplateParams(), getIdentifier(), getDiscriminator(),
         getRawDataLocation(), getRawAssociated(), getRawAllocated(),
-        getRawRank(), getAnnotations());
+        getRawRank(), getAnnotations(), getNumExtraInhabitants());
   }
 
 public:
@@ -1222,11 +1249,11 @@ class DICompositeType : public DIType {
        StringRef Identifier = "", DIDerivedType *Discriminator = nullptr,
        Metadata *DataLocation = nullptr, Metadata *Associated = nullptr,
        Metadata *Allocated = nullptr, Metadata *Rank = nullptr,
-       DINodeArray Annotations = nullptr),
+       DINodeArray Annotations = nullptr, uint32_t NumExtraInhabitants = 0),
       (Tag, Name, File, Line, Scope, BaseType, SizeInBits, AlignInBits,
-       OffsetInBits, Flags, Elements, RuntimeLang, VTableHolder, TemplateParams,
-       Identifier, Discriminator, DataLocation, Associated, Allocated, Rank,
-       Annotations))
+       OffsetInBits, NumExtraInhabitants, Flags, Elements, RuntimeLang,
+       VTableHolder, TemplateParams, Identifier, Discriminator, DataLocation,
+       Associated, Allocated, Rank, Annotations))
   DEFINE_MDNODE_GET(
       DICompositeType,
       (unsigned Tag, MDString *Name, Metadata *File, unsigned Line,
@@ -1236,11 +1263,12 @@ class DICompositeType : public DIType {
        Metadata *TemplateParams = nullptr, MDString *Identifier = nullptr,
        Metadata *Discriminator = nullptr, Metadata *DataLocation = nullptr,
        Metadata *Associated = nullptr, Metadata *Allocated = nullptr,
-       Metadata *Rank = nullptr, Metadata *Annotations = nullptr),
+       Metadata *Rank = nullptr, Metadata *Annotations = nullptr,
+       uint32_t NumExtraInhabitants = 0),
       (Tag, Name, File, Line, Scope, BaseType, SizeInBits, AlignInBits,
        OffsetInBits, Flags, Elements, RuntimeLang, VTableHolder, TemplateParams,
        Identifier, Discriminator, DataLocation, Associated, Allocated, Rank,
-       Annotations))
+       Annotations, NumExtraInhabitants))
 
   TempDICompositeType clone() const { return cloneImpl(); }
 
@@ -1255,8 +1283,8 @@ class DICompositeType : public DIType {
   getODRType(LLVMContext &Context, MDString &Identifier, unsigned Tag,
              MDString *Name, Metadata *File, unsigned Line, Metadata *Scope,
              Metadata *BaseType, uint64_t SizeInBits, uint32_t AlignInBits,
-             uint64_t OffsetInBits, DIFlags Flags, Metadata *Elements,
-             unsigned RuntimeLang, Metadata *VTableHolder,
+             uint64_t OffsetInBits, uint32_t NumExtraInhabitants, DIFlags Flags,
+             Metadata *Elements, unsigned RuntimeLang, Metadata *VTableHolder,
              Metadata *TemplateParams, Metadata *Discriminator,
              Metadata *DataLocation, Metadata *Associated, Metadata *Allocated,
              Metadata *Rank, Metadata *Annotations);
@@ -1272,15 +1300,14 @@ class DICompositeType : public DIType {
   ///
   /// If not \a LLVMContext::isODRUniquingDebugTypes(), this function returns
   /// nullptr.
-  static DICompositeType *
-  buildODRType(LLVMContext &Context, MDString &Identifier, unsigned Tag,
-               MDString *Name, Metadata *File, unsigned Line, Metadata *Scope,
-               Metadata *BaseType, uint64_t SizeInBits, uint32_t AlignInBits,
-               uint64_t OffsetInBits, DIFlags Flags, Metadata *Elements,
-               unsigned RuntimeLang, Metadata *VTableHolder,
-               Metadata *TemplateParams, Metadata *Discriminator,
-               Metadata *DataLocation, Metadata *Associated,
-               Metadata *Allocated, Metadata *Rank, Metadata *Annotations);
+  static DICompositeType *buildODRType(
+      LLVMContext &Context, MDString &Identifier, unsigned Tag, MDString *Name,
+      Metadata *File, unsigned Line, Metadata *Scope, Metadata *BaseType,
+      uint64_t SizeInBits, uint32_t AlignInBits, uint64_t OffsetInBits,
+      uint32_t NumExtraInhabitants, DIFlags Flags, Metadata *Elements,
+      unsigned RuntimeLang, Metadata *VTableHolder, Metadata *TemplateParams,
+      Metadata *Discriminator, Metadata *DataLocation, Metadata *Associated,
+      Metadata *Allocated, Metadata *Rank, Metadata *Annotations);
 
   DIType *getBaseType() const { return cast_or_null<DIType>(getRawBaseType()); }
   DINodeArray getElements() const {